Veterinary Medicine/Domestication

Rattus Norvegicus, the Norway rat, is also known as the Asian Brown Rat, the Brown Rat and the Barn Rat, and is the species of domesticated pet and laboratory rats as well as the common city "sewer" rat. These animals are not nocturnal but semi-nocturnal, or crepuscular, like cats. While they are "up and down" all the time, they are generally dozy during the day, becoming active at dusk. Their close relative, Rattus Rattus -- the Asian Black Rat, Ship Rat or Roof Rat -- is more truly nocturnal: nearly comatose during the day and has developed an automatic bite reflex if disturbed in the nest during sleep cycles.